An amorphous solid is a solid that does not exhibit the long-range order characteristics of a crystal and as a result has no crystalline structure in the solid phase. A nanocomposite crystalline solid with very small grain size can also be categorized as amorphous as long as the grain size is in the order of a couple of nanometers. In the early 1960's, there was extensive interest in the development of amorphous magnetic materials, such as Permalloy, to lower the energy loss in transformers and energy generation. Recently, the interest has shifted toward nanocomposite materials which exhibit a certain level of crystallinity without achieving the amorphous content of materials such as glass. This shift in interest has led to materials with superior properties and consequently to new fields of application.
The non-homogeneity of feedstock, whether it is solid or liquid, and the non-uniform thermal path during material processing have been two key problems when producing homogeneous and amorphous materials. Nanocerox, Inc. produced magnesia-yttria nanocomposites suitable in the fabrication of domes. These nanocomposites are not amorphously produced and are used in the infrared transmission after consolidation. Nanocerox powders are produced using a flame pyrolysis method, described in U.S. Pat. No. 5,958,361, which uses a relatively low temperature not exceeding 1500° C. while conventional plasma processes can reach temperatures well above a couple of thousand degrees Celsius. The initial non-homogeneity in the molecular composition of the solids is exacerbated because of the non-uniform thermal paths found in most conventional plasma spray processes, such as arc-plasma processes. These non-uniform thermal paths are due to the non-uniform temperature profiles found across the plasma plume. Even when using solution precursors, which have the advantage of uniformity in the initial material composition, subsequent thermal treatment remains an issue, because of the side-injection of solutes for example, which inherently subjects the processed material to non-uniform thermal paths. This leads to non-homogeneity and non-amorphous products or coatings.
The present invention solves the issue of composition non-homogeneity of feedstock and non-uniform thermal paths by creating a uniform melt state using the microwave plasma spray process. This uniform melt state is achieved by combining several key elements which include: axial injection, uniform solution precursor droplets with droplet diameter range variations no greater than 5% and a uniform plasma temperature profile in an axis-symmetric thermal processing environment. This uniform melt state process is characterized by high heating rates followed by high quenching rates. This leads to homogenous thermal processing along a uniform thermal path of the uniform composition of materials which results in homogenous and amorphous powder materials.
Thus there is a need to produce homogenous and amorphous powders using a plasma processing method which can provide a uniform high temperature thermal path for all the feed materials processed. However, no such method has been reported.
From the above, it is therefore seen that there exists a need in the art to overcome the deficiencies and limitations described herein and above.